Who sings theme song for Mr Sunshine show?

The theme song for the Korean drama "Mr. Sunshine" is sung by Kim Tae-yeon, the lead vocalist of the South Korean girl group Girls' Generation. The song is titled "Into the New World" (새로운 세상, Sae로운 Sesang) and is a powerful and emotive ballad that perfectly captures the drama's themes of love, loss, and sacrifice.